Used Cars in Cochin - Where to Search for?

One of my friend needs a second hand car and he was searching for the last couple of months, but in vain. He couldn't find a car that matches his requirement and budget. He also contacted me regarding the availability of used cars, and we both went to several places to see different cars. But still my friend is not satisfied with them due to different reasons.

He is actually looking out for used Maruti cars, and in Cochin the chances of getting a good used Maruti car is more than in the rural areas. I have heard that there are certain showrooms in Cochin which sells used cars, but am not sure which one is the best. I see a lot of advertisements in the newspaper regarding showrooms which offers second hand cars for sale in Cochin.

Is it worthy buying cars from these showrooms, or should we need to take a mechanic along with us while visiting the showroom to check the condition of these cars. Do these showrooms do basic services on these cars before selling? If anybody have any idea about the best used car showroom in Cochin, please let me know through the comment section. The guy is looking for  Maruti models such as Alto and Zen which are in good condition and his budget is around 1.5 lakhs.